RDW: What Your Results Mean
Bottom line: RDW measures variation in red blood cell size. Normal is up to 14.5%. High RDW suggests mixed causes of anemia or nutritional deficiencies.
What Is RDW (Red Cell Distribution Width)?
RDW stands for Red Cell Distribution Width. It's a measurement that tells your doctor about the variation in the size of your red blood cells. Think of it like a collection of marbles: RDW is a way to see if all your marbles are roughly the same size, or if there's a big mix of very small and very large ones.
Red blood cells are vital for carrying oxygen throughout your body. Normally, they are all about the same size. An elevated RDW means there's a wider range of sizes among your red blood cells than usual, while a low RDW means they are more uniform. This variation can be an early indicator of certain underlying medical conditions, particularly different types of anemia, and helps doctors differentiate between them.
RDW (Red Cell Distribution Width) Reference Ranges
| Classification | Range (%) |
|---|---|
| Very Low | 8.5 - 11.0 |
| Low | 11.0 - 13.0 |
| Normal | 13.0 - 14.5 |
| High | 14.5 - 16.0 |
| Very High | 16.0 - 18.0 |
What Affects Your RDW (Red Cell Distribution Width) Levels?
- Iron deficiency anemia
- Vitamin B12 deficiency anemia
- Folate deficiency anemia
- Chronic liver disease
- Recent blood transfusion
- Certain inherited blood disorders (like thalassemia)
- Certain types of infections
- Pregnancy
When to Get Tested
The RDW test is typically ordered as part of a complete blood count (CBC), which is a common blood test used to evaluate your overall health. It is frequently used by doctors when investigating the cause of anemia, especially if other blood count parameters suggest that the red blood cells are not uniform in size. It can also be ordered as a routine part of a physical examination or if you are experiencing symptoms like fatigue, weakness, or pale skin.
Look Up Your RDW (Red Cell Distribution Width) Result
Select your value below to see a detailed breakdown of what it means:
Read the Full Blood Test Guide
Frequently Asked Questions
A high RDW means your red blood cells vary significantly in size. This can indicate various types of anemia, such as iron deficiency anemia or vitamin B12/folate deficiency anemia, or other conditions affecting red blood cell production.
A low RDW means your red blood cells are very uniform in size. While generally considered less concerning than a high RDW, it can sometimes be seen in certain conditions or immediately after a blood transfusion when the transfused cells are all the same size.
Yes, it is possible for RDW to be elevated even before overt anemia develops. An increased RDW can be an early sign that your body is having difficulty producing healthy red blood cells, potentially due to a developing deficiency like iron or vitamin B12.
